It is known from German Auslegeschrift No. 1,190,184 that difunctional or polyfunctional cyanic acid esters may be polymerized to form high molecular weight polytriazines. The polymerization reaction, which is highly exothermic, takes place by way of a so-called "B-stage" and is accompanied by a fairly considerable shrinkage (Kunststoff-Handbuch, Vol. 58, page 829 (1968)). This gives rise to various disadvantages, including inadequate dimensional stability of the thus-produced moldings. According to British Pat. No. 1,305,762, these disadvantages may be obviated by interrupting the polymerization reaction by cooling after a prepolymer has formed, i.e. after from about 30 to 65% of the cyanic acid ester groups have reacted.
German Offenlegungsschrift No. 2,360,709 relates to a process for the production of triazine prepolymers in which aromatic dihydroxyl or polyhydroxyl compounds are initially condensed with less than 1/3 mol of cyanuric chloride per hydroxyl group and the free hydroxyl groups in the thus-obtained condensation product are subsequently reacted with a halogen cyanide in the presence of a base.